The present invention relates generally to exposure, and more particularly to an exposure apparatus and method that exposes an object, such as a single crystal substrate for a semiconductor wafer, and a glass plate for a liquid crystal display (“LCD”).
Along with the recent demands for smaller and lower profile electronic devices, the finer processing of the semiconductor devices to be mounted onto these electronic devices has been increasingly demanded. For example, a design rule attempts to form a circuit pattern of 100 nm or less, and it is expected to shift to a formation of circuit patterns of 80 nm or less in the future. The mainstream photolithography technology has conventionally used a projection exposure apparatus that projects and transfers a pattern on a mask (a reticle) onto a wafer.
The minimum critical dimension to be transferred by the projection exposure apparatus (resolution) is proportionate to a wavelength of light used for exposure, and inversely proportionate to the numerical aperture of the projection optical system. Therefore, the short wavelength of the exposure light and the high NA of the projection optical system have been promoted but they are not enough to satisfy the demand for the finer processing.
Accordingly, the technology that forms an effective light source distribution optimal to a reticle pattern (or the modified illumination) has now attracted attention. The effective light source distribution is formed by driving plural elements in the illumination optical system. A driven position of each element is stored or calculated as a device parameter. The “effective light source”, as used herein, means an angular distribution of the exposure light incident upon the wafer surface or a light intensity distribution on the pupil surface in the projection optical system. The effective light source distribution is formed by desirably shaping the light intensity distribution on the pupil surface in the projection optical system or a Fourier transformed surface of the reticle surface, such as a surface near the exit surface of the fly-eye lens. The modified illumination generally uses an annular illumination, a dipole illumination, a quadruple illumination, etc.
The repetitive exposures often cause absorptions of the exposure light energy and thermal deformations of the projection optical system, and a variance of its performance (such as the imaging magnification, imaging position, curvature of field, distortion, spherical aberration, and astigmatism) as a result of the heat radiation, deteriorating the imaging performance. The prior art proposes a method that includes the steps of calculating a variance amount of the exposure performance of the projection optical system using, as parameters, the total dose of the light that transmits the reticle pattern, the necessary exposure time period, and the time interval between exposures in addition to the time constant peculiar to the projection optical system, and correcting the variance amount through controls over driving of the wafer stage, driving of the projection lens, pressure between lenses, and fine adjustments of the wavelength of the exposure light. See, for example, Japanese Patent No. 3,186,011.
The exposure apparatus can, for example, previously store various correction amounts of the projection optical system corresponding to the effective light source distributions (such as the imaging magnification, imaging position, curvature of field, distortion, spherical aberration, and astigmatism during exposure), and use these correction amounts for the exposure. In exposure, it is sufficient only to select the optimal effective light source distribution for a reticle pattern, and the various correction amounts corresponding to the effective light source distribution do not have to be considered during the exposure.
The recent technology enables a diffraction optical element, such as a computer generated hologram (“CGH”) to form a desired effective light source distribution, and mount, for example, the diffraction optical element that forms a new effective light source distribution, onto an exposure apparatus at an arbitrary timing.
However, an effective light source distribution formed by the newly mounted diffraction optical element may possibly deteriorate the imaging performance and yield, because the exposure apparatus does not store the corresponding correction amount.